Ground ring purpose
- Thread starter Sahib
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fmtjfw
Senior Member
- Location
- Fairmont, WV, USA
It's another method of grounding (driven rods, UFER, metal water pipe).
It may be useful in providing a better ground for lightning.
I would not trust anything to prevent step potential problems during a lightning strike.
It may be useful in providing a better ground for lightning.
I would not trust anything to prevent step potential problems during a lightning strike.
K8MHZ
Senior Member
- Occupation
- Electrician
Ground rings are designed to protect buildings and equipment, not people.
From Wiki:
From Wiki:
- Location
- Illinois
- Occupation
- retired electrician
The ground ring in the National Electrical Code is not required...it is just one of a number of types of grounding electrodes that are permitted to be used in cases where you are required to install a grounding electrode.
- Location
- Massachusetts
To add to what Don pointed out I will point out the NEC is about property protection as well.
K8MHZ
Senior Member
- Occupation
- Electrician
Also note that 90.1 addresses safeguarding from the use of electricity. It does not say safeguarding from lightning.
Well this is one of my specialties and my answer is on the technical merits and purpose of a ground ring application and has nothing to do with NEC Code other than NEC permits the use of ground rings.
In a building like a DATA CENTER, TELEPHONE SWITCHING OFFICE, or MILITARY COMMUNICATION CENTER using a GROUND RING has nothing to do with Lightning Protection SYSTEM. In fact it is NOT and should NOT be used although some mistakenly do out of ignorance. The down conductors for a LPS should be bonded to driven rods outside the perimeter of the ground ring, not to the ground ring as some believe. The Ground Ring and LPS are bonded together at one point and one point only with a bonding jumper outside near the AC service entry point which is usually an extension of the ground electrode conductor. The purpose of the Ground Ring in such facilities facilitates obtaining the infamous 5 ohm or less ground impedance, and allows for bonding multiple entrance point ground bars of services like Outside Plant Cabling, radio tower entrances for the wave-guides and coaxes keeping the required bonding outside away from the building allowing lightning surge potential differences to a minimum and bleed away to earth rather than taking it inside the building. In such installation a direct strike to the LPS with a Ground Ring does provide a Shunt Effect around the building similar to a Farady Cage Effect in that it reduces Step Potential Differences inside the ring, but is mostly a moot point because most of those facilities also use a massive UFER or NEC CCE ground electrode forming a equipotential ground plane.
Moving onto radio and cell towers those facilities are not normally manned but employ ground rings, so the argument of life safety is a moot point, it is about the equipment and does serve in lightning protection, but not the way you might be thinking. In a equipment shelter, one that has a door and walls you walk into employs a Ground Ring and a HALO GROUND RING. The ground Ring is installed in the usual manner encircling the building with a couple of added modifications where at each corner of the building a ground rod is driven and bonded to the ring and at the coax hatch plate and AC service entrance points. Then inside the building a Ground Halo Ring is installed on the exterior 4 walls with isolators about 4 to 6 inches below the ceiling line. At each corner the Halo is bonded to the outside Ground Ring. The purpose of the Halo Ground Ring is to attenuate EMP when the tower is directly struck by lighting keeping it out of the equipment inside the shelter.
The only place I know of where a Ground Ring is installed and used for life safety really has nothing to do with an Electrical Service Installation. I do a lot of this for Mission work with my church in places like Africa, India Cuba, and other poor undeveloped countries involving mud huts used for homes. In the tropical regions when thunderstorms occur lighting strikes nearby objects like tree and the gradient step potential difference injur or kill the occupants inside the mud huts if they happen to be standing or touching the ground inside on two or more points. This is how lightning injures or kills people even in the USA. You do not have to be hit directly, just unfortunate enough to be close to an object that is struck. Anyway the solution is real simple, a Ground Ring ran around the mud huts. It does not even have to be electrical wire, any kind of wire will do as is often the case in poor countries. We have used bob wire, mattress wire, bailing wirie, and scrap telephone wire. What even works better is chain link fence inside the hut buried below the surface a few inches making a equipotential ground plane. There is the word again, ground plane. As the ring does in this case with or without electrical service is provide a Shunt around the hut minimizing step potential differences. Every place we have istalled one there has not been a injury or fatality since from lightning when inside a protected hut.
Anyway I hope that helps explain why rings are sometimes used. Unfortunately they are often misused out of ignorance which negate any benefit of using them.
In a building like a DATA CENTER, TELEPHONE SWITCHING OFFICE, or MILITARY COMMUNICATION CENTER using a GROUND RING has nothing to do with Lightning Protection SYSTEM. In fact it is NOT and should NOT be used although some mistakenly do out of ignorance. The down conductors for a LPS should be bonded to driven rods outside the perimeter of the ground ring, not to the ground ring as some believe. The Ground Ring and LPS are bonded together at one point and one point only with a bonding jumper outside near the AC service entry point which is usually an extension of the ground electrode conductor. The purpose of the Ground Ring in such facilities facilitates obtaining the infamous 5 ohm or less ground impedance, and allows for bonding multiple entrance point ground bars of services like Outside Plant Cabling, radio tower entrances for the wave-guides and coaxes keeping the required bonding outside away from the building allowing lightning surge potential differences to a minimum and bleed away to earth rather than taking it inside the building. In such installation a direct strike to the LPS with a Ground Ring does provide a Shunt Effect around the building similar to a Farady Cage Effect in that it reduces Step Potential Differences inside the ring, but is mostly a moot point because most of those facilities also use a massive UFER or NEC CCE ground electrode forming a equipotential ground plane.
Moving onto radio and cell towers those facilities are not normally manned but employ ground rings, so the argument of life safety is a moot point, it is about the equipment and does serve in lightning protection, but not the way you might be thinking. In a equipment shelter, one that has a door and walls you walk into employs a Ground Ring and a HALO GROUND RING. The ground Ring is installed in the usual manner encircling the building with a couple of added modifications where at each corner of the building a ground rod is driven and bonded to the ring and at the coax hatch plate and AC service entrance points. Then inside the building a Ground Halo Ring is installed on the exterior 4 walls with isolators about 4 to 6 inches below the ceiling line. At each corner the Halo is bonded to the outside Ground Ring. The purpose of the Halo Ground Ring is to attenuate EMP when the tower is directly struck by lighting keeping it out of the equipment inside the shelter.
The only place I know of where a Ground Ring is installed and used for life safety really has nothing to do with an Electrical Service Installation. I do a lot of this for Mission work with my church in places like Africa, India Cuba, and other poor undeveloped countries involving mud huts used for homes. In the tropical regions when thunderstorms occur lighting strikes nearby objects like tree and the gradient step potential difference injur or kill the occupants inside the mud huts if they happen to be standing or touching the ground inside on two or more points. This is how lightning injures or kills people even in the USA. You do not have to be hit directly, just unfortunate enough to be close to an object that is struck. Anyway the solution is real simple, a Ground Ring ran around the mud huts. It does not even have to be electrical wire, any kind of wire will do as is often the case in poor countries. We have used bob wire, mattress wire, bailing wirie, and scrap telephone wire. What even works better is chain link fence inside the hut buried below the surface a few inches making a equipotential ground plane. There is the word again, ground plane. As the ring does in this case with or without electrical service is provide a Shunt around the hut minimizing step potential differences. Every place we have istalled one there has not been a injury or fatality since from lightning when inside a protected hut.
Anyway I hope that helps explain why rings are sometimes used. Unfortunately they are often misused out of ignorance which negate any benefit of using them.
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So it looks like a simple logic to assume that if lightning current originates outside a ground area covered by a metal ground ring, that area becomes more or less eqipotential and on the other hand if the lightning current originates inside the area, the ground area outside to it becomes more or less eqipotential and may be safe to tread on only for that particular lightning current. Hence my belief stated in the OP.
beanland
Senior Member
- Location
- Vancouver, WA
Personnel Safety
Personnel Safety
IEEE 80 addresses step and touch potential and a ground ring is often used around medium-voltage equipment to reduce the touch potential when switching medium voltage equipment.
For a building where the electrical resistivity of the native soil is poor, achieving good grounding requires long lengths of conductor in contact with the ground. A ground ring can be a cost effective way to get better grounding.
Personnel Safety
IEEE 80 addresses step and touch potential and a ground ring is often used around medium-voltage equipment to reduce the touch potential when switching medium voltage equipment.
For a building where the electrical resistivity of the native soil is poor, achieving good grounding requires long lengths of conductor in contact with the ground. A ground ring can be a cost effective way to get better grounding.
- Location
- Illinois
- Occupation
- retired electrician
For other than the types of applications Dereck talked about in post #8, what purpose does "better grounding" serve?
In MV and HV Sub-stations they use grids. Any equipment where personnel are likely to be like a switch or cabinet will have a raised steel platform bonded to the grid installed for the person to stand on. NESC requires the ground grid to be extended a minimum of 10 feet beyond the fence line last time I checked. But keep in mind MV and HV do not behave like LV of 600 volts or less where ground is useless as a conductor.
By better ground is meant safer ground as a safe ground provides a degree of 1)product safety and 2)human safety.
- Location
- Illinois
- Occupation
- retired electrician
How does a better ground, (connection to earth) make the system safer?
It is rather a better grounding design than a better connection ( i.e a lower resistance) to earth that makes the system safer.
- Location
- Massachusetts
And how does this lower resistance to earth make the system safer?
I did not say that in my last post.
The lower grounding resistance has a role to play substation grounding and lightning protection.
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Ground resistance has very little if anything to do a good LPS. A 10 foot section of 750 MCM exhibits roughly 3K ohms of impedance at lightning frequencies. Does not make one bit of difference if the earth electrode is 1 or 100 ohms if it is in series with 3K ohms. Either way you still have 3K ohms.
As for a sub-station even though they are designed to obtain 10-Ohms, anything 200 ohms or less is more than adequate to operate the switch gear. However that has nothing to do with life safety as not even a 1 Ohm ground would save your life, it would only make you vaporize faster.
- Location
- Massachusetts
No. In the post of mine you quoted I said I would prefer a ground system of good design over one with simply low ground resistance
Its exactly what you said in the post of yours I quoted. Now you are backpeddeling.
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